Wafer Boat

Abstract

A wafer boat for transporting multiple wafers is disclosed. [Solution] The wafer boat comprises a bottom member, an upper member, and at least three rods, each extending between the bottom member and the upper member and comprising a plurality of wafer supports. Each rod is provided with a stress control notch region for limiting thermal stress between the rod and the bottom member.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to the field of semiconductor processing methods, as well as related structures and apparatuses, and to the field of device and integrated circuit manufacturing. More specifically, the present disclosure generally relates to wafer carriers for use in batch semiconductor processing apparatuses.

BACKGROUND ART

[0002] In the field of semiconductor manufacturing, wafer boats are critical components of batch processing apparatuses, including but not limited to vertical furnaces. These boats are designed to hold a plurality of semiconductor wafers simultaneously during processes that may be performed at high temperatures, and play a vital role in achieving the desired throughput for commercial production.

[0003] The ability to accommodate more wafers without compromising the stability of the boat is an important consideration. Stability is essential not only to ensure uniform processing of all wafers, but also to reduce the risk of mechanical failure during operation. A wafer boat must maintain its structural integrity while being subjected to mechanical handling and high thermal gradients characteristic of semiconductor processing. The operating environment of these wafer boats often includes high-temperature processes exceeding 1000°C, as are common in oxidation and diffusion processes. Prolonged exposure to such extreme temperatures causes significant thermal stress in the wafer boat. This stress can lead to material deformation, cracking, or other forms of degradation, which in turn compromises the uniformity and quality of the semiconductor wafers being processed.

[0004] As a result, the development of wafer boats with enhanced thermal stability and resistance to high-temperature stress is an important challenge in the industry.

[0005] Any discussions described in this section, including discussions of problems and solutions, are included in this disclosure solely for the purpose of providing background to this disclosure, and it should not be considered that any or all of the discussions were known at the time the invention was made, or that they constitute prior art. [Overview of the project]

[0006] This summary introduces the selected concepts in a simplified form, which are described in more detail below. This summary is not necessarily intended to identify the main or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0007] According to a first aspect of the present invention, a wafer boat for transporting a plurality of wafers is provided, comprising a bottom member, an upper member, and at least three rods, each rod extending between the bottom member and the upper member, and comprising a plurality of wafer supports, each rod comprising a stress control notch region for limiting thermal stress between the rod and the bottom member.

[0008] By including stress-controlled notch regions, boats according to embodiments of the present invention may exhibit improved resistance to large temperature gradients. Boats according to embodiments of the present invention may be able to withstand higher temperature gradients without damage compared to a standard boat that does not include stress-controlled notch regions.

[0009] In some embodiments, the stress-controlled notch region is provided between the bottom member and the support in the plurality of wafer supports closest to the bottom member.

[0010] In some embodiments, the bottom member and the top member are spaced apart in a first direction, and each rod, at the wafer support position, has a length in a second direction perpendicular to the first direction that exceeds its length in a third direction perpendicular to both the first and second directions.

[0011] In some embodiments, the maximum length of the rod in the second direction is at least three times the maximum length of the rod in the third direction.

[0012] In some embodiments, the notch is provided to shorten the length of the rod in a second direction at the location of the notch.

[0013] In some embodiments, the length of the rod in the second direction at the notch position is 20% to 70% of the length of the rod in the second direction at the wafer support position.

[0014] In some embodiments, the notches are provided on a first side of the boat rod and on a second opposite side of the boat rod, with the first and second sides spaced apart in the second direction.

[0015] In some embodiments, each notch on the rod has substantially the same shape.

[0016] In some embodiments, no notches are provided at the location of the notches that shorten the length of the rod in a third direction.

[0017] In some embodiments, each rod includes an additional stress control notch region to limit thermal stress between the rod and the upper member.

[0018] In some embodiments, additional stress control notch regions are provided between the upper member and the supports in the plurality of wafer supports closest to the upper member.

[0019] In some embodiments, the multiple wafer supports are finger-shaped.

[0020] In some embodiments, the wafer boat is made of silicon.

[0021] In some embodiments, the wafer boat includes at least 100 wafer supports.

[0022] Other technical configurations will also be readily apparent to those skilled in the art from the following drawings, description, and claims.

[0023] For the purpose of summarizing the present invention and the advantages achieved over the prior art, certain objects and advantages of the present invention have been described above in this specification. It will be appreciated that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the present invention. Thus, for example, those skilled in the art will recognize that the present invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein, without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0024] All of these embodiments are intended to be within the scope of the invention disclosed herein. These and other embodiments will be readily apparent to those skilled in the art from the following detailed description of certain specific embodiments, with reference to the accompanying drawings, and the present invention is not limited to any particular embodiment disclosed. [Brief Description of the Drawings]

[0025] Specific embodiments of the present invention will now be described by way of example with reference to the accompanying drawings.

[0026] [Figure 1] It is a perspective view of a boat according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view in a vertical plane of a rod included in a boat according to an embodiment of the present invention and having a notched region at a lower portion. [Figure 3] It is a view of a boat according to an embodiment of the present invention along a first direction toward a bottom member, viewed from a point between the bottom member and an upper member. [Figure 4] It is a top view of a support that may be included in a boat according to an embodiment of the present invention. [Figure 5]This is a cross-sectional view of the rod at the position in the first direction corresponding to the position of the notch region. [Figure 6] This is a cross-sectional view in the vertical plane of the rod included in the boat according to the embodiment of the present invention and having notch regions at the lower portion and the upper portion. [Figure 7] This is a plot of the maximum von Mises yield condition divided by the yield stress as a function of the maximum temperature for two boats according to an embodiment of the present invention, which also shows a reference plot for a boat that does not include a stress relaxation notch region.

[0027] It will be appreciated that elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help improve understanding of the illustrated embodiments of the present disclosure. MODE FOR CARRYING OUT THE INVENTION

[0028] The description of the exemplary embodiments of the methods and configurations provided below is merely exemplary and is intended for illustrative purposes only. The following description is not intended to limit the scope of the present disclosure or the claims. Furthermore, the description of multiple embodiments having the illustrated configurations or steps is not intended to exclude other embodiments having additional configurations or steps, or other embodiments incorporating different combinations of the stated configurations or steps.

[0029] In the present disclosure, when two or more elements are referred to as being "in fluid communication", it means that a fluid such as a gas, a liquid, or a mixture thereof can flow between the elements in one direction or both directions. Fluid communication may be achieved, for example, by means of gas lines, tubes, pipes, inlets, outlets, or any combination thereof. Fluid communication may be interruptable, for example, a valve or other flow control element may be present.

[0030] In this disclosure, any two-digit variable can constitute a viable range for that variable, and any range shown may include or exclude endpoints. Furthermore, any value of a shown variable (whether shown with "approximately" or not) may refer to an exact value, an approximate value, or its equivalent, and in some embodiments may refer to the mean, median, measure of central tendency, major value, etc. Furthermore, in this disclosure, the terms “including,” “constituted by,” and “having” may independently mean “typically or broadly comprising,” “comprising,” “consisting essentially of,” or “consisting of” in some embodiments. In this disclosure, no defined meaning necessarily excludes the ordinary and customary meanings in some embodiments. In some cases, the percentages expressed herein may be relative or absolute.

[0031] Through the embodiments of this disclosure, many exemplary materials are given, and it should be noted that the chemical formulas given for each of the exemplary materials should not be interpreted as restrictive, and that the non-restrictive exemplary materials given should not be limited by any exemplary stoichiometry.

[0032] In this specification, the terms “on” or “over” may be used to describe relative positional relationships. Another element, membrane, or layer may be directly on top of the layer described, or another layer (intermediate layer) or element may be interposed between them, or a layer may be placed on top of the layer described, but not necessarily completely covering the surface of the layer described. Thus, unless the term “directly” is used otherwise, the terms “on” or “over” will be interpreted as relative concepts. Similarly, it will be understood that the terms “under,” “underlying,” or “below” will be interpreted as relative concepts.

[0033] Referring to Figures 1, 2, and 3, a wafer boat 101 for transporting multiple wafers according to an embodiment of the present invention comprises a bottom member 102 and an upper member 103, which are spaced apart in a first direction z. The bottom member 102 and the upper member 103 are generally circular in shape and may include a central region 104 from which material is removed. This can help reduce thermal stress on the bottom member 102 and the upper member 103 when subjected to large temperature changes.

[0034] The wafer boat 101 comprises at least three rods 105. Each rod 105 extends between the bottom member 102 and the upper member 103. Referring particularly to Figures 1 and 3, the rods 105 are positioned to provide a wafer insertion opening 106 into which a wafer can be inserted in the boat in the wafer insertion direction 107. In some embodiments, one of the rods 105 may be positioned in the wafer insertion direction 107 and may be referred to as the back rod, while the other rods 105 are referred to as side rods. In some embodiments, the at least three rods 105 include at least four rods 105.

[0035] Each rod 105 comprises a plurality of wafer supports 108. The wafer supports 108 are spaced apart in a first direction to provide a plurality of positions in a plane perpendicular to a first direction in which a wafer can be supported. The supports 108 may be provided by forming notches 109 in the rod 105, while the body 110 of the rod 105 remains without notches 109. The supports 108 may be formed by providing projections extending from the body 110 of the rod 105. The supports 108 may be spaced evenly apart in the first direction, i.e., the distance between one support and an adjacent support on the same rod 105 does not have to differ between pairs of adjacent supports. The wafer boat 101 may comprise at least 100, at least 120, or at least 140 supports 108 per rod 105. The wafer boat 101 may be made of silicon.

[0036] Each rod 105 includes an upper part 111 to which the rod 105 is attached to the upper member 103, and a lower part 112 to which the rod 105 is attached to the bottom member 102. The rods 105 may be attached using joining methods such as adhesive, welding, or bolting. The upper part 111 and the lower part 112 do not necessarily include the support 108. The upper part 111 is provided between the uppermost support 113 of the support 108 and the upper member 103. The lower part 112 is provided between the lowermost support 114 of the support 108 and the bottom member 102.

[0037] Each rod 105 is provided with a stress control notch region 115 for limiting thermal stress between the rod 105 and the bottom member 102. The stress control notch region 115 is a region of the rod 105 from which material is removed such that the cross-section of the rod in a plane perpendicular to a first direction at the location of the stress control notch region 115 is different from the cross-section of the rod in a plane perpendicular to a first direction at a location away from the notch region. The stress control notch region 115 may be provided in the lower part 112. By providing the stress control notch region 115, stress on the bottom member 102 at high temperatures, for example, due to uneven cooling of the wafer boat 101 and / or deformation of the rod 105, can be reduced. While not bound by theory, it is conceivable that by removing material from the rod 105 in a controlled manner within the notched region(s), the rod 105 would have increased flexibility at high temperatures and behave as an expansion joint, allowing it to withstand an increased amount of bending without damaging the bottom member 102 compared to a rod without the stress-controlled notched region 115.

[0038] Each support 108 may have a finger-type shape in a plane perpendicular to the first direction. For example, referring to Figure 4, each rod may have a first length L1 at a wafer support position in a second direction y perpendicular to the first direction z, and a second length L2 at a wafer support position in a third direction x perpendicular to both the first direction z and the second direction y, where the first length L1 may exceed the second length L2. The wafer support positions are positions along the first direction in which the wafer supports are provided. The wafer support positions are not positions along the first direction in which gaps (e.g., notches 109) are provided between wafer supports, or positions along the first direction in which stress control notch regions 115 are provided.

[0039] The cross-sectional profile of the rod 105 in a plane perpendicular to the first direction may be the same as the shape shown in Figure 4 at positions away from the gap between wafer supports and away from the stress control notch regions 115 and 120.

[0040] In some embodiments, the first length L1 may vary along a third direction, for example, by a corner rounding process. In some embodiments, the second length L2 may vary along a second direction, for example, by rounding and / or tapering the corners toward the end of the support 108. However, the minimum value of the first length L1 may always be greater than the maximum value of the second length L2. The minimum value of the first length L1 may be at least twice, at least three times, or at least four times the maximum value of the second length L2. By providing a finger-shaped support 108, it may be possible to reduce slippage between the wafer and the support, for example, in high-temperature processes.

[0041] The stress control notch region 115 may be provided as a single notch region within each rod. The stress control notch region 115 may include a first notch region 116 on one edge of the rod 105 and a second notch region 117 on the opposite edge of the rod 105. The first notch region 116 and the second notch region 117 may be spaced apart in a second direction. The first notch region 116 and the second notch region 117 may be made on opposing edges 118, 119 of the rod 105, respectively, and the opposing edges 118, 119 may be spaced apart in a second direction. The first notch region 116 and the second notch region 117 may be provided at substantially the same position in the first direction. In some embodiments, the first notch region 116 and / or the second notch region 117 may form an open notch in the rod 105. The first notch region 116 and the second notch region 117 may have substantially the same shape. The first notch region 116 and the second notch region 117 may have different shapes.

[0042] In some embodiments, stress control notches 115, for example, a first notch 116 and a second notch 117, are provided to shorten the length of the rod 105 in a second direction at the location of the notch. The reduction in length may be constant or vary over the height of the stress control notch 115. For example, the stress control notch 115 may be longer in the second direction at points closer to the bottom member 102 than at points farther from the bottom member 102. This may help to provide the rod 105 with greater stability.

[0043] In some embodiments, the length L3 of the rod 105 in the second direction at the location of the stress control notch region 115 is shorter than the length L1 of the rod 105 in the second direction at the location of the lower part 112 between the bottom member 102 and the stress control notch region 115 in the first direction, and is shorter than the length of the rod in the second direction at the location of the lower part 112 between the stress control notch region 115 and the lowest support 114 in the first direction.

[0044] In some embodiments, the length L3 of the rod 105 in the second direction at the location of the notch region 115 is 20% to 70% of the length L1 of the rod 105 in the second direction at the location of the lower part 112 between the bottom member 102 and the stress control notch region 115 in the first direction, and is 20% to 70% of the length of the rod in the second direction at the location of the lower part 112 between the stress control notch region 115 and the lowest support 114 in the first direction.

[0045] In some embodiments, the length L3 of the rod 105 in the second direction at the location of the stress control notch region 115 is 20% to 40% of the length L1 of the rod 105 in the second direction at the location of the lower part 112 between the bottom member 102 and the stress control notch region 115 in the first direction, and is 20% to 40% of the length of the rod in the second direction at the location of the lower part 112 between the stress control notch region 115 and the lowest support 114 in the first direction.

[0046] In some embodiments, the length L3 of the rod 105 in the second direction at the location of the stress control notch region 115 is 40% to 60% of the length L1 of the rod 105 in the second direction at the location of the lower part 112 between the bottom member 102 and the stress control notch region 115 in the first direction, and 40% to 60% of the length of the rod in the second direction at the location of the lower part 112 between the stress control notch region 115 and the lowest support 114 in the first direction.

[0047] In some embodiments, the length L3 of the rod 105 in the second direction at the location of the stress control notch region 115 is 30% to 40% of the length L1 of the rod 105 in the second direction at the location of the lower part 112 between the bottom member 102 and the stress control notch region 115 in the first direction, and is 30% to 40% of the length of the rod in the second direction at the location of the lower part 112 between the stress control notch region 115 and the lowest support 114 in the first direction.

[0048] The stress control notch region 115 may generally be square, rectangular, circular, elliptical, or any other preferred shape. In some embodiments, a single stress control notch region 115 may be provided on each rod 105. A single stress control notch region 115 may be provided, for example, on the edge 119 of a rod 105 that is oriented away from the central axis A of the boat.

[0049] Preferably, one or more stress control notches 115 are provided to shorten the length of the rod 105 at the location of the stress control notch only in the second direction. The length L4 of the rod in the third direction at the location of the notch may change along the second direction due to the tapering of the rod 105, but not due to the provision of any notch. In other words, the length L4 of the rod in the third direction at the location of the notch may be the same as the length of the rod in the third direction at the wafer support position, and both measurements are performed at the same location in the xy plane.

[0050] Stress control notches 115, for example, a first notch 116 and a second notch 117, may each have a height H1 in the first direction that exceeds the distance D in the first direction between adjacent wafer supports on the rod 105. For example, the height H1 may be at least twice, at least three times, or at least four times the distance D. The height H1 of the stress control notch 115 may be selected to balance the increased flexibility provided by increasing the height of the stress control notch 115 with the undesirable increase in the thermal gradient caused by such an increase in height.

[0051] Referring to Figure 6, in some embodiments, each rod 105 includes an additional stress control notch region to limit thermal stress between the rod 105 and the upper member 103. The additional stress control notch region may be referred to as the upper notch region 120. The upper notch region 120 is a region of the rod 105 from which material is removed such that the cross-section of the rod in a plane perpendicular to a first direction at the location of the upper notch region 120 is different from the cross-section of the rod in a plane perpendicular to a first direction at a location away from the upper notch region 120. The upper notch region 120 may be provided on the upper 111. By providing the upper notch region (additional stress control notch region) 120, stress on the upper member 103 at high temperatures, for example, due to uneven cooling of the wafer boat 101 and / or deformation of the rod 105, can be reduced.

[0052] The upper notch region 120 may be provided as a single notch region within each rod. The upper notch region 120 may include a first upper notch region 121 on one edge of the rod 105 and a second upper notch region 122 on the opposite edge of the rod 105. The first upper notch region 121 and the second upper notch region 122 may be spaced apart in a second direction. The first upper notch region 121 and the second upper notch region 122 may be formed on opposing edges 118, 119 of the rod 105, respectively, and the opposing edges 118, 119 may be spaced apart in a second direction. The first upper notch region 121 and the second upper notch region 122 may be located substantially in the same position in the first direction. In some embodiments, the first upper notch region 121 and / or the second upper notch region 122 may form an open notch in the rod 105. In some embodiments, the first upper notch region 121 and / or the second upper notch region 122 may be through holes for the rod 105. The first upper notch region 121 and the second upper notch region 122 may have substantially the same shape. The first upper notch region 121 and the second upper notch region 122 may have different shapes.

[0053] In some embodiments, upper notch regions 120, for example, a first upper notch region 121 and a second upper notch region 122, are provided to shorten the length of the rod 105 in a second direction at the location of the notch region. The reduction in length may be constant or vary over the height of the upper notch region 120. For example, the length of the upper notch region 120 in the second direction may be longer at points closer to the upper member 103 than at points farther from the upper member 103. This may help to provide the rod 105 with greater stability.

[0054] In some embodiments, the length of the rod 105 in the second direction at the location of the upper notch region 120 is shorter than the length of the rod 105 in the second direction at the location of the upper part 111 between the upper member 103 and the upper notch region 120 in the first direction, and is shorter than the length of the rod in the second direction at the location of the upper part 111 between the upper notch region 120 and the uppermost support 113 in the first direction.

[0055] In some embodiments, the length of the rod 105 in the second direction at the location of the upper notch region 120 is 20% to 70% of the length of the rod 105 in the second direction at the location of the upper part 111 between the upper member 103 and the upper notch region 120 in the first direction, and 20% to 70% of the length of the rod in the second direction at the location of the upper part 111 between the upper notch region 120 and the uppermost support 113 in the first direction.

[0056] In some embodiments, the length of the rod 105 in the second direction at the location of the upper notch region 120 is 20% to 40% of the length of the rod 105 in the second direction at the location of the upper part 111 between the upper member 103 and the upper notch region 120 in the first direction, and 20% to 40% of the length of the rod in the second direction at the location of the upper part 111 between the upper notch region 120 and the uppermost support 113 in the first direction.

[0057] In some embodiments, the length of the rod 105 in the second direction at the location of the upper notch region 120 is 40% to 60% of the length of the rod 105 in the second direction at the location of the upper part 111 between the upper member 103 and the upper notch region 120 in the first direction, and 40% to 60% of the length of the rod in the second direction at the location of the upper part 111 between the upper notch region 120 and the uppermost support 113 in the first direction.

[0058] In some embodiments, the length of the rod 105 in the second direction at the location of the upper notch region 120 is 30% to 40% of the length of the rod 105 in the second direction at the location of the upper part 111 between the upper member 103 and the upper notch region 120 in the first direction, and 30% to 40% of the length of the rod in the second direction at the location of the upper part 111 between the upper notch region 120 and the uppermost support 113 in the first direction.

[0059] The upper notch region 120 may generally be square, rectangular, circular, elliptical, or any preferred shape. In some embodiments, a single upper notch region 120 may be provided on each rod 105. A single upper notch region 120 may be provided, for example, on the edge 119 of a rod 105 that is oriented away from the central axis A of the boat.

[0060] The upper notch region or region 120 is preferably provided to shorten the length of the rod 105 at the location of the additional stress control notch region, only in the second direction. The length of the rod L4 in the third direction at the location of the notch may change along the second direction due to the tapering of the rod 105, but not due to the provision of any notch. In other words, the length of the rod L4 in the third direction at the location of the notch may be the same as the length of the rod in the third direction at the wafer support position, and both measurements are taken at the same location in the xy plane.

[0061] The notched regions (or multiple regions) 120, for example, the first upper notched region 121 and the second upper notched region 122, may each have a height in the first direction that exceeds the distance D in the first direction between adjacent wafer supports on the rod 105. For example, the height may be at least twice, at least three times, or at least four times the distance D.

[0062] The stress control notch region 115 and / or the upper notch region 120 may include two or more notches spaced apart in the first direction, while all notches in the stress control notch region 115 remain between the lowest support 114 and the bottom member 102, and all notches in the upper notch region 120 remain between the uppermost support 113 and the upper member 103.

[0063] Referring to Figure 7, the results of finite element thermomechanical simulations of two boats according to embodiments of the present invention are shown, along with a reference boat. The boats according to embodiments of the present invention include a boat having a stress-controlled notch region only at the lower 112, as shown in Figure 2, and a boat having stress-controlled notch regions at both the lower 112 and upper 111, as shown in Figure 6. All boats have 119 slots per rod. The reference boat does not have a stress-controlled notch region. For each temperature value, the thermomechanical behavior of the boat was calculated for the process of heating the boat to that temperature and then cooling the boat. The maximum von Mises stress criterion divided by the yield stress is shown as a function of maximum temperature. It can be seen that for all temperature values ​​of both boats according to embodiments of the present invention, the ratio is reduced compared to the reference boat. In some cases, it may be preferable to have a stress-controlled notch region only at the lower 112, as including a stress-controlled notch region at the upper 111 may necessitate reducing the number of wafer support positions that could affect throughput.

[0064] For the purpose of summarizing the advantages of the present invention and the advantages achieved over the prior art, certain objectives and advantages of the present invention are described above herein. Naturally, it will be understood that not all of these objectives or advantages are necessarily achieved according to any particular embodiment of the present invention. Therefore, those skilled in the art will recognize that the present invention may be embodied or practiced in a manner that achieves or optimizes one or a group of advantages as taught or suggested herein, without necessarily achieving other objectives or advantages as taught or suggested herein.

[0065] All of these embodiments are intended to be within the scope of the present invention disclosed herein. These and other embodiments will be readily apparent to those skilled in the art from the following detailed description of certain embodiments with reference to the accompanying drawings, but the present invention is not limited to any particular embodiment disclosed. [Explanation of Symbols]

[0066] 101 Wafer Boat 102 Bottom member 103 Upper member 105 Rod 108 wafer support 115 Stress-controlled notch region

Claims

1. A wafer boat for transporting multiple wafers, comprising a bottom member, an upper member, and at least three rods, each of which extends between the bottom member and the upper member, and comprising a plurality of wafer supports, each of which includes a stress control notch region for limiting thermal stress between the rod and the bottom member.

2. The wafer boat according to claim 1, wherein the stress control notch region is provided between the bottom member and the support in the plurality of wafer supports closest to the bottom member.

3. The wafer boat according to claim 1 or 2, wherein the bottom member and the upper member are spaced apart in a first direction, and the length of each rod in a second direction perpendicular to the first direction at the wafer support position exceeds the length in a third direction perpendicular to both the first and second directions at the wafer support position.

4. The wafer boat according to claim 3, wherein the shortest length of the rod in the second direction is at least three times the maximum length of the rod in the third direction.

5. The wafer boat according to claim 3, wherein the stress control notch region is provided to shorten the length of the rod in the second direction at the location of the stress control notch region.

6. The wafer boat according to claim 5, wherein the length of the rod in the second direction at the location of the stress control notch region is 20% to 70% of the length of the rod in the second direction at the wafer support position.

7. The wafer boat according to claim 5, wherein the stress control notch region is provided on a first side of the boat rod and on a second side opposite to the boat rod, and the first side and the second side are spaced apart in the second direction.

8. The wafer boat according to claim 7, wherein each of the stress control notch regions on the rod has the same shape.

9. The wafer boat according to claim 3, wherein no notch region is provided at the location of the stress control notch region that shortens the length of the rod in the third direction.

10. The wafer boat according to claim 1, wherein each of the rods comprises an additional stress control notch region for limiting thermal stress between the rod and the upper member.

11. The wafer boat according to claim 10, wherein the additional stress control notch region is provided between the upper member and the support in the plurality of wafer supports closest to the upper member.

12. The wafer boat according to claim 1, wherein the plurality of wafer supports are finger-shaped.

13. A wafer boat according to claim 1, comprising silicon.

14. A wafer boat according to claim 1, comprising at least 100 wafer supports.

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